Crunchyroll is a great place to start. It depends on what you're looking for, if you want subbed Crunchyroll is a great place to go to see anime that are currently airing as well.
Funimation has a streaming service, and have recently partnered with Crunchyroll to create an app called Vrv. You can find more dubbed anime on Funimation. Viz is also a great place to check out some shows. They are great places to browse when looking for something new to watch.
Netflix often carries the more popular series that have either been around for a while, or they have some rights to. Hulu is another place you can go as well, as they tend to differ slightly from what Netflix has.